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RF cabling...

Discussion in 'Cables & Switches' started by bwgames, Mar 8, 2005.

  1. bwgames

    bwgames
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    A few questions please?
    When we first moved into this house, we got some builders (as well as other things) to install some RF cabling from the upstairs location of Sky Box, via this room (PC room, for capturing stuff) down to the living room.
    We also got them to install some composite video and L/R audio cables from the Sky box to this room, for higher quality AV capture.
    Since then I've installed a S-Video cable from the Sky box to this PC, and am planning on a PVR-250 for decent MPEG2 DVD capture.

    Now.... What we've done is to watch telly via RF from the sky box downstairs, but, we've needed a booster to get a decent signal:
    a) This shouldn't be neccessary? Its 15/20 metres I'd say.
    b) In this room, what the builders have done is to take two RF cables:

    Sky box <-----> TV outlet < --same tv outlet, just attached another cable to the same outlet> to TV outlet downstairs.
    I've been told that this is a awful way to do it, impendance etc?
    Is there a way to recable this to negate the need for the booster?
    There is no way I can replace the cabling, as it goes in the walls, but maybe I could do something in this room?

    But, onto the real point of this post:

    We're getting sick of having to go upstairs to change the channel (TV link doesn't work, due to the booster, but thats another issue), and there was previous NTL cabling to the downstairs telly from the previous owners.
    The quality is awful, but I think thats due to the poor quality of the co-ax from the NTL box,which I'm replacing in the near future.

    What I want to do is this...

    Downstairs, connect the NTL co-ax to the same wire that goes to the Sky Box, meaning that upstairs, where the sky box is, and in this room, (as well as downstairs) I can *tune* into the normal UHF channels from the NTL co-ax, as well as the Sky Box on RF channel 68 or something. (I can capture from Sky using the S-Video cable, so thats not a problem in here, but I'd like to be able to tune into UHF channels from NTL in here, so I can watch something other than whats on Sky.)

    Is this possible?

    to have:

    Sky ---> this room ----> downstairs, and, on the same cable, ntl co-ax ---> sky cabling --> Sky + NTL UHF on the same cable.


    Thanks,
    Ben
     
  2. vex

    vex
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    Urrrrm.

    Let me try to answer this, but I need to ask a few questions first.

    1) Do you have a tv aerial? If yes does it come in on the connection that the sky box RF1 or RF2 is connecting in on and then going on to the other rooms?

    2) Do you know if there is a signal present on the NTL cable?

    Some initial answers!

    Did you specify the cable that your builder was to use? My guess is not so he has installed cheap as chips C55 type cable which used to be used as standard aerial cable but is about as good as a bit of wet string.

    The cable may also be damaged, kinked or crushed in the build process which will have a dramatic effect on the signal. This can only really be check using a TDR test equipment

    I also suspect that if you have a TV aerial and you are trying to 'add in' the sky out signal then this mixing is degrading the signal.

    OK, Adding NTL, If there is a signal present then it could be cut off at any time, however if you are still prepared to do the work then you really need to know what channels (frequencies) the system uses because if it does 'conflict' with the Sky channel you are running then you will get the same interference problem.

    WRT the sky eyes not working, there is a work around, but you also need to make sure that the faceplates you are connecting to are NOT isolated. This is tricky as most older houses are fitted with isolated plates. Isolated plates block the power passing through it, which means the eye will not power up. You also need to 'turn on' the sky eye function within the sky box and make sure you are connected to the RF2 output of the SKy Box.

    One quick check, if you plug in the eye directly into the back of the RF2 on the back of the sky box, does the red LED come on? If yes it is receiving power if not, then there is not power coming out of your box.

    Long Post, but hope it helps
     
  3. bwgames

    bwgames
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    No, not standard terrestial, this is why we want the NTL cable, to enable us to tune into other channels without having to make everyone watch whats on the sky box
    Yes there is, albeit faint, but I'm going to recable the cabling from the wall box to the TV in the hope it'll fix it

    No, I'll have to check what type it is, thanks for that...

    That is what I was wondering with the 'join' in the middle outlet, whether that degraded it enough...


    That is essentially what I am trying to do with the NTL cable.
    I have already tuned the downstairs TV into it, and am confident I can re-arrange the Sky box to fit around the available NTL channels -they are poor quality, but I reckon that's due to the outside cabling - its been left unused for several years (2/3), which is why I'm planning on replacing it.


    All of this was done two years ago, which should be modern enough?
    The sky eye works fine on the downstairs telly, IF I don't use the booster, but I need the booster for a decent signal = the problem. I could get a booster that was sky link compatible, but I shouldn't need to, I don't think, not for this short a length?
    All that works fine, see above....


    Thanks for that, its helped but my main concern is whether I can physically have two input signals (at different frequencies) at either end of a cable, and I would be able to get the signal of both at the other end?

    Attached a quick diagram to this post...

    Thanks.
     

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  4. vex

    vex
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    Ok I understand,

    In theory there is nothing to stop you doing that at all. It is exactly how the return path in cable tv works. Two different frequencies, pumped in at opposite ends of the same cable.

    However it does set a few alarm bells of caution in my head.

    1) not sure how the NTL system / network people would like to have another channel shoved up thier cable system. Chance are they will not spot it, but you could equally have them knocking on your door blaming you for shed loads if interferance.

    2) Equally NTL certainly will not like have a voltage (passing from the SKy box RF2) pass up thier cable.

    3) Replacing the NTL cable may be harder than it looks, especially if it is terminated in the tradiditonal CATV Cabinet, I suspect the fault is not the cable but a poor disconnection at thier end is the cause of the weak signal.

    4) Make sure you are a good number of channel spaces away from any of the NTL channels to minimise interference. 3 as a minimum

    Thats it for now, hope it helps.

    Chris
     
  5. bwgames

    bwgames
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    Ah....
    1 + 2) Good point, I hadn't thought about that.....

    What about using a VCR in the way? NTL in, standard RF out, that wouldn't interfere with the NTL network?

    3) Well, the cable i'm referring to is from the wall box on my house to the TV, its easy enough to change that, I'm just hoping the problem isn't in the underground cable, as nawt I can do then.
     

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